A popular type of refrigerant compressor for use in vehicle air conditioning systems involves a wobble or nutating drive mechanism to provide infinitely variable displacement. In this type of compressor, a plurality of cylinders are equally angularly spaced about a cylinder block and housing, and equally radially spaced from the axis of a central drive hub. A piston is mounted for reciprocating motion in each of the cylinders. A piston rod connects each piston to a non-rotatable socket or wobble plate that provides the nutating motion in response to a rotating drive shaft included in the central drive hub. The driving of the socket plate in a nutating path serves to impart the linear reciprocating motion to the pistons, thereby providing proper compressor operation. By varying the angle of the socket plate relative to the drive hub, through internal refrigerant gas pressure, the stroke of the pistons and, therefore, the displacement or capacity of the compressor is varied.
The action of the nutating socket plate in the refrigerant compressor inherently results in it being subjected to torque. In order for the compressor to properly function, the torque applied to the socket plate must be properly restrained; i.e. an equal and opposite torque must be transmitted to a fixed structure, such as to the compressor housing. A common method of restraining torque found in prior art socket plate compressors involves the use of guide pin/slider assembly such as that disclosed in U.S. Pat. No. 4,480,964 to Skinner, issued Nov. 6, 1984. The guide pin is fixed to the cylinder block and a ball guide is slidably mounted thereon and retained on the socket plate. The guide pin thus prevents the socket plate from rotating with the rotary drive plate and allows the torque applied to the socket plate to be restrained by transmitting an equal and opposite torque through the cylinder block to the fixed housing.
This torque restraint design for compressors undesirably produces torsional oscillations. It can be appreciated that the axis of the socket plate does not coincide with the axis of the drive hub, but rather varies through a variety of angular positions with respect to the drive hub as it travels in its nutating path. As a result of the variation of the angular relationship between the drive hub and the socket plate, as the non-rotating socket plate wobbles or nutates, a torsional acceleration and deceleration action results in the drive shaft. The torsional oscillation resulting from the alternating acceleration and deceleration of the drive shaft occurs twice per hub revolution. This torsional oscillation creates undesirable vibration within the compressor.
Thus, while this prior art torque restraint design for compressors has thus proved generally effective, there is some need for improvement to alleviate the vibration problem. More specifically, there is a need to provide a mechanism that prevents socket plate rotation without inducing torsional oscillation in the drive shaft. One approach to solving this problem is disclosed in the co-pending U.S. application entitled RZEPPA JOINT SOCKET PLATE TORQUE RESTRAINT ASSEMBLY FOR A VARIABLE DISPLACEMENT COMPRESSOR, filed Apr. 5, 1990 , Ser. No. 07/504,817 and assigned to the assignee of the present invention. A spherical Rzeppa constant velocity joint is described as being utilized to uniformly restrain the socket plate motion relative to the drive mechanism, and thus prevent vibration. As is known, the Rzeppa joint by itself cannot accommodate the axial change of position of the socket plate as it operates through its range of motion. To perform this function according to this previous invention, a co-axial anti-rotation shaft is provided. It is keyed to the housing and slides axially to accommodate compressor adjustment between full and zero displacement.
Improvements to the socket plate torque restraint mechanism are appropriate to refine the operation. One area showing promise for improvement is concerned with efficiently accommodating this axial change of position of the socket plate. The ideal socket plate torque restraint mechanism prevents rotation in a manner such that the inertial torque reaction about the axis of the compressor drive hub and shaft is, or approaches, zero at any instant. The socket plate torque restraint mechanism produces an equal and opposite torque to that applied to the socket plate and carries it to a ground or fixed structure, such as the housing, within the compressor assembly. Such a socket plate torque restraint mechanism would be inexpensive, and at the same time very efficient in eliminating the deleterious vibration of the compressor. Its key parts would have features easier to machine, assemble and maintain.